This invention relates in general to bearings for supporting shafts for rotation. In particular, this invention relates to an improved structure for a center bearing assembly for rotatably supporting an intermediate portion of a vehicle driveshaft assembly.
In most land vehicles in use today, a drive train system is provided for transmitting rotational power from an output shaft of an engine/transmission assembly to an input shaft of an axle assembly so as to rotatably drive one or more wheels of the vehicle. To accomplish this, a typical vehicular drive train system includes a driveshaft assembly having first and second end fittings (such as tube yokes) that are secured to the opposed ends thereof. The first end fitting forms a portion of a first universal joint, which provides a rotatable driving connection from the output shaft of the engine/transmission assembly to the first end of the driveshaft assembly while accommodating a limited amount of angular misalignment between the rotational axes thereof. Similarly, the second end fitting forms a portion of a second universal joint, which provides a rotatable driving connection from the second end of the driveshaft assembly to the input shaft of the axle assembly while accommodating a limited amount of angular misalignment between the rotational axes thereof.
In some vehicles, the distance separating the engine/transmission assembly and the axle assembly is relatively short. For these vehicles, the driveshaft assembly can be formed from a single, relatively long driveshaft tube having the first and second end fittings secured to the ends thereof. In other vehicles, however, the distance separating the engine/transmission assembly and the axle assembly is relatively long, making the use of a single driveshaft tube impractical. For these vehicles, the driveshaft assembly can be formed from a plurality (typically two) of separate, relatively short driveshaft sections. In a compound driveshaft assembly such as this, a first end of the first driveshaft section is connected to the output shaft of the engine/transmission assembly by a first universal joint, a second end of the first driveshaft section is connected to a first end of the second driveshaft section by a second universal joint, and a second end of the second driveshaft section is connected to the input shaft of the axle assembly by a third universal joint.
A compound driveshaft assembly that is composed of two or more separate driveshaft sections usually requires the use of a structure for supporting the intermediate portions thereof for rotation during use. A typical intermediate support structure for a driveshaft assembly (which is typically referred to as a center bearing assembly) includes an annular bearing having an inner race that engages one of the driveshaft sections and an outer race that supports the inner race for rotation relative thereto. The outer race of the annular bearing is supported within a generally annular support member that is usually formed from a relatively resilient material, such as rubber. The resilient support member is, in turn, supported within a rigid bracket that is secured to a support surface provided on the vehicle. Thus, the center bearing assembly functions to support the intermediate portion of the driveshaft assembly for rotation during use. Many center bearing assembly structures of this general type are known in the art.
As is well known, the engine/transmission assembly of a typical vehicular drive train system generates a variety of torsional and other relatively high frequency vibrations in the driveshaft assembly as it is rotated during use. Such driveshaft assembly vibrations often result in the generation of noise that can undesirably be transmitted into the vehicle. The resilient support member is provided in the center bearing assembly to absorb at least some of such vibrations so as to reduce the amount of noise that is transmitted from the driveshaft assembly to the vehicle frame. To accomplish this, the resilient support member is usually formed from an elastomeric material, such as rubber, having a resonant frequency that is approximately the same as the frequency of the vibrations that are generated in the driveshaft assembly. When the resonant frequency of the resilient support member is approximately the same as the frequency of the noise and other vibrations in the driveshaft assembly, then such noise and other vibrations will be substantially absorbed by the resilient support member and will not transmitted to the vehicle frame during use.
However, it has been found that the resonant frequency of the resilient support member may not always be approximately the same as the frequency of the noise and other vibrations in the driveshaft assembly. For example, it has been found that changes in the ambient temperature of the resilient support member can cause the resonant frequency thereof to vary. However, the torsional and other relatively high frequency vibrations that are generated by the engine and the transmission in the driveshaft assembly as it is rotated during use remain relatively constant. If the resonant frequency of the resilient support member is not approximately the same as the frequency of the noise and other vibrations in the driveshaft assembly, then the ability of the resilient support member to absorb such noise and other vibrations will be adversely affected. Thus, it would be desirable to provide a resilient support member for a center bearing assembly having a resonant frequency that can be adjusted in accordance with changes in the operating conditions of the vehicle such that the resonant frequency of the resilient support member is always approximately the same as the frequency of the noise and other vibrations in the driveshaft assembly. Therefore, noise and other vibrations will be substantially absorbed by the resilient support member and will not transmitted to the vehicle frame during use.